The steroid hormone cortisol is a key regulator of many physiological processes. However, an excess of cortisol, as occurs in Cushing's Disease, provokes severe metabolic abnormalities including: type 2 diabetes, cardiovascular disease, obesity, and osteoporosis. Many patients with these diseases, however, do not show significant increases in plasma cortisol levels. In addition to plasma cortisol, individual tissues can regulate their glucocorticoid tone via the in situ conversion of inactive cortisone to the active hormone cortisol. Indeed, the normally high plasma concentration of cortisone provides a ready supply of precursor for conversion to cortisol via the intracellular enzyme 11-beta-hydroxysteroid dehydrogenase type I (11-beta-HSD1).
11-beta-HSD1 is a member of the short chain dehydrogenase superfamily of enzymes. By catalyzing the conversion of biologically inactive cortisone to cortisol, 11-beta-HSD1 controls the intracellular glucocorticoid tone according to its expression and activity levels. In this manner, 11-beta-HSD1 can determine the overall metabolic status of the organ. 11-beta-HSD1 is expressed at high levels in the liver and at lower levels in many metabolically active tissues including the adipose, the CNS, the pancreas, and the pituitary. Taking the example of the liver, it is predicted that high levels of 11-beta-HSD1 activity will stimulate gluconeogenesis and overall glucose output. Conversely, reduction of 11-beta-HSD1 activity will downregulate gluconeogenesis resulting in lower plasma glucose levels.
Various studies have been conducted that support this hypothesis. For example, transgenic mice expressing 2× the normal level of 11-beta-HSD1 in only the adipose tissue show abdominal obesity, hyperglycemia, and insulin resistance. (H. Masuzaki, J. Paterson, H. Shinyama, N. M. Morton, J. J. Mullins, J. R. Seckl, J. S. Flier, A Transgenic Model of Visceral Obesity and the Metabolic Syndrome, Science 294:2166-2170 (2001). Conversely, when the 11-beta-HSD1 gene is ablated by homologous recombination, the resulting mice are resistant to diet induced obesity and the accompanying dysregulation of glucose metabolism (N. M. Morton, J. M. Paterson, H. Masuzaki, M. C. Holmes, B. Staels, C. Fievet, B. R. Walker, J. S. Flier, J. J. Mullings, J. R. Seckl, Novel Adipose Tissue-Mediated Resistance to Diet-induced Visceral Obesity in 11β-Hydroxysteroid Dehydrogenase Type 1-Deficient Mice. Diabetes 53: 931-938 (2004). In addition, treatment of genetic mouse models of obesity and diabetes (ob/ob, db/db and KKAy mice) with a specific inhibitor of 11-beta-HSD1 causes a decrease in glucose output from the liver and an overall increase in insulin sensitivity (P. Alberts, C. Nilsson, G. Selen, L. O. M. Engblom, N. H. M. Edling, S. Norling, G. Klingstrom, C. Larsson, M. Forsgren, M. Ashkzari, C. E. Nilsson, M. Fiedler, E. Bergqvist, B. Ohman, E. Bjorkstrand, L. B. Abrahmsen, Selective Inhibition of 11β-Hydroxysteroid Dehydrogenase Type I Improves Hepatic Insuling Sensuitivity in Hyperglycemic Mice Strains, Endocrinology 144: 4755-4762 (2003)). Based in part on these studies, it is believed that local control of cortisol levels is important in metabolic diseases in these model systems. In addition, the results of these studies also suggest that inhibition of 11-beta-HSD1 will be a viable strategy for treating metabolic diseases such as type 2 diabetes, obesity, and the metabolic syndrome.
Lending further support to this idea are the results of a series of preliminary clinical studies. For example, several reports have shown that adipose tissue from obese individuals has elevated levels of 11-beta-HSD1 activity. In addition, studies with carbenoxolone, a natural product derived from licorice that inhibits both 11-beta-HSD1 and 11-beta-HSD2 (converts cortisol to cortisone in kidney) have shown promising results. A seven day, double blind, placebo controlled, cross over study with carbenoxolone in mildly overweight individuals with type 2 diabetes showed that patients treated with the inhibitor, but not the placebo group, displayed a decrease in hepatic glucose production (R. C. Andrews, O. Rooyackers, B. R. Walker, J. Clin. Endocrinol. Metab. 88: 285-291 (2003)). This observation is consistent with the inhibition of 11-beta-HSD1 in the liver. Furthermore, another clinical study reported that the inhibition of 11-beta-HSD1 may provide a novel treatment option for patients with glaucoma (Rauz et al., IOVS, Vol. 42, No. 9, pp. 2037-2042 (August 2001)). The results of these preclinical and early clinical studies strongly support the concept that treatment with a potent and selective inhibitor of 11-beta-HSD1 will be an efficacious therapy in patients afflicted with various disorders.